New Methodology to Determine Work Zone Capacity Distribution

Since the true value of work zone capacity is difficult to be known with a perfect confidence, work zone capacity should be represented by means of a probability distribution. Therefore, this study proposes a methodology to determine work zone capacity distribution based on the probabilistic speed-flow relationships. Firstly, the traffic speed and flow are modeled as random variables following the lognormal distribution. Subsequently, the lognormal distributed speed-flow functions are established to formulize the probabilistic speed-flow relationships under the uncongested and congested traffic conditions, respectively. Finally, a work zone capacity distribution model is derived based on the probabilistic speed-flow relationships. One case study using the observed traffic data from Singapore work zones is carried out to testify the effectiveness of the proposed methodology. The effects of related to work zone configuration like the geometrical alignment and speed limit on the mean and prediction interval of work zone capacity are examined in the case study. The proposed methodology could help traffic engineers evaluate the variability of work zone capacity and the reliability of traffic management strategies.